1. Field of the Invention
The present invention relates to Public Land Mobile Network (PLMN) search and selection technologies in a mobile communication device. More particularly, the present invention relates to a mobile communication device having a plurality of Subscriber Identification Module (SIM) cards and methods for searching for a PLMN for each SIM card in the mobile communication device.
2. Description of the Related Art
A mobile communication device performs a process of selecting a Public Land Mobile Network (PLMN) in order to start a mobile communication service. Namely, when powered on, the mobile communication device searches for PLMNs located nearby in order to allow a mobile communication service to select a PLMN with the highest priority. Once a PLMN with the highest priority is found, the mobile communication device performs a location registration. Here, the PLMN with the highest priority is often referred to as a home PLMN (HPLMN), and information about HPLMN is stored as International Mobile Subscriber Identity (IMSI) information in a Subscriber Identification Module (SIM) card. If the mobile communication device fails to find the HPLMN and therefore performs a location registration by selecting a PLMN other than the HPLMN, the device considers a location-registered PLMN as a Visited PLMN (VPLMN) and periodically searches for a PLMN with a higher priority than the VPLMN. If any PLMN with a higher priority than a currently registered VPLMN is found, the mobile communication device performs a location registration with the found PLMN.
During a PLMN search, the mobile communication device performs a scanning at regular intervals. A scanning cycle is stored as a higher priority PLMN search period (EF_HPPLMN) of a SIM card. When registered in any VPLMN, the mobile communication device searches for the HPLMN at such a scanning cycle.
The mobile communication device that has a plurality of SIM cards searches for PLMNs independently for each SIM card according to scanning cycles stored in the SIM cards.
FIG. 1 shows a technique to search for a PLMN in a mobile communication device having a plurality of SIM cards in accordance with the related art.
Referring to FIG. 1, the mobile communication device starts HPLMN timers independently for SIM 1 and SIM 2, and then performs a PLMN search at the expiry of each HPLMN timer. In the example shown in FIG. 1, the mobile communication device searches for a PLMN according to a scanning cycle (e.g., 30 minutes) stored in the SIM 1 and also searches for a PLMN according to another scanning cycle (e.g., 60 minutes) stored in the SIM 2.
Normally a PLMN search causes an increase of power consumption. Since the mobile communication device having a plurality of SIM cards starts the HPLMN timers independently according to HPLMN timer values stored in the respective SIM cards and then performs a PLMN search at the expiry of each HPLMN timer, relatively greater power consumption may be caused in comparison with a mobile communication device having a single SIM card.